Adaptive antenna array methods and apparatus for use in a multi-access wireless communication system

Abstract

Adaptive antenna array techniques for use in an orthogonal frequency division multiplexed spread-spectrum multi-access (OFDM-SSMA) cellular wireless system or other type of wireless communication system. A base station of the system includes an antenna array and a base station receiver. The base station receiver implements an adaptive antenna gain algorithm which estimates a spatial covariance matrix for each of K mobile stations communicating with the base station. The spatial covariance matrix for a given one of the mobile stations is determined at least in part based on a unique hopping sequence of the mobile station, and provides a correlation between signals received from the mobile station at different antenna elements within the antenna array. An average spatial covariance matrix for a set of received signals is also generated. The individual spatial covariance matrices and the average spatial covariance matrix are processed to generate an estimate of an interference matrix for the K mobile stations, and the estimate of the interference matrix is further processed to generate array responses for each of the mobile stations. The array response for a given mobile station is processed to determine an antenna weighting which is applied to a signal received from the given mobile station in order to facilitate detection of a corresponding transmitted symbol.

1. A method for providing adaptation of an antenna array in a base station associated with a cell of a cellular wireless communication system, comprising the steps of:
 estimating a spatial covariance matrix for each of a plurality of mobile stations communicating with the base station, the spatial covariance matrix for a given one of the mobile stations being determined at least in part based on a unique hopping sequence of the mobile station and providing a correlation between signals received from the mobile station at different antenna elements within the antenna array;  
 processing the estimated spatial covariance matrices to generate an estimate of an interference matrix for the plurality of mobile stations;  
 estimating an array response for the given mobile station from the interference matrix;  
 processing the array response for the given mobile station to generate an antenna weighting associated with the given mobile station; and  
 applying the antenna weighting to a signal received from the given mobile station in order to facilitate detection of a corresponding transmitted symbol.  
 
   
   
     2. The method of  claim 1  wherein the cellular wireless system comprises an orthogonal frequency division multiplexed (OFDM) system with spread spectrum multiple access (SSMA). 
   
   
     3. The method of  claim 1  wherein the antenna array comprises M antenna elements, and the spatial covariance matrices and the interference matrix each comprise an M×M matrix. 
   
   
     4. The method of  claim 1  wherein the array response comprises a scaled array response vector. 
   
   
     5. The method of  claim 1  further including the steps of selecting initial estimates for the interference matrix and the array responses for each of the plurality of mobile stations, and subsequently applying a designated number of iterations of an iterative algorithm to determine final estimates of the interference matrix and the array responses for each of the plurality of mobile stations. 
   
   
     6. The method of  claim 1  wherein the step of estimating the spatial covariance matrix for each of the plurality of mobile stations further comprises computing a spatial covariance matrix {circumflex over (P)} z (k) of a signal z(t,k)=y(t,σ(t,k)), where t denotes a particular symbol period, k=1, . . . K denotes a particular one of K mobile stations communicating with the base station within the symbol period, y(t,n) denotes the received signal for symbol period t and tone index n=1, . . . N, and σ(t,k) denotes the unique hopping sequence for the kth mobile station. 
   
   
     7. The method of  claim 6  wherein the spatial covariance matrix {circumflex over (P)} z (k) is estimated for the kth mobile station after receipt of T symbols of data in accordance with the following equation: 
             P   ^     z     ⁡     (   k   )       =       1   T     ⁢       ∑     t   =   1     T     ⁢           ⁢       z   ⁡     (     t   ,   k     )       ⁢         z   ⁡     (     t   ,   k     )       *     .               
 
   
   
     8. The method of  claim 6  further including the steps of estimating a spatial covariance matrix for each of the signals y(t,n), n=1, . . . , N, and then averaging the resulting N estimated spatial covariance matrices to obtain an estimated M×M average received spatial covariance matrix {circumflex over (P)} y . 
   
   
     9. The method of  claim 6  wherein the estimated average received spatial covariance matrix {circumflex over (P)} y  is estimated after receipt of T symbols of data in accordance with the following equation: 
           P   ^     y     =       1   TN     ⁢       ∑     t   =   1     T     ⁢           ⁢       ∑     n   =   1     N     ⁢           ⁢       y   ⁡     (     t   ,   n     )       ⁢         y   ⁡     (     t   ,   n     )       *     .                 
 
   
   
     10. The method of  claim 6  wherein the estimated spatial covariance matrices {circumflex over (P)} z (k), k=1, . . . , K, and the average received spatial covariance matrix {circumflex over (P)} y  are processed to compute estimates {circumflex over (b)} k  for a scaled array response vector b k , and an estimate {circumflex over (P)} w  for an interference spatial covariance matrix P w . 
   
   
     11. The method of  claim 10  wherein the step of processing the array response for the given mobile station to generate an antenna weighting associated with the given mobile station further includes generating a set of antenna weight vectors c(t,k)={circumflex over (P)} w   −1 {circumflex over (b)} k  for k=1, . . . , K. 
   
   
     12. The method of  claim 10  wherein the estimates for the array response b k  and the interference spatial covariance matrix P w  are determined by solving the following equations
     P   z ( k )= b   k   b   k   *+P   w   , k =1 , . . . , K ,          P   y     =       P   w     +       1   N     ⁢       ∑     k   =   1     K     ⁢           ⁢       b   k     ⁢         b   k     *     .                   
 
     with the estimates {circumflex over (P)} z (k) and {circumflex over (P)} y  inserted in place of P z (k) and P y  and using an approximate iterative algorithm. 
   
   
     13. The method of  claim 12  wherein the iterative algorithm updates stored estimates {circumflex over (b)} k , k=1, . . . , K, for the scaled array response vectors b k  in each iteration. 
   
   
     14. The method of  claim 13  wherein the update is performed in each iteration by first estimating the interference spatial covariance matrix by summing outer products {circumflex over (b)} k {circumflex over (b)} k * and then subtracting the sum from {circumflex over (P)} y  to yield the estimate 
           P   ^     w     =         P   ^     y     -       1   N     ⁢       ∑     k   =   1     K     ⁢           ⁢         b   ^     k     ⁢           b   ^     k     *     .                 
 
     and then, for each k=1, . . . , K, updating the vectors {circumflex over (b)} k  by the assignment
   v k ←({circumflex over (P)} z (k)−{circumflex over (P)} w ){circumflex over (b)} k ,  
   {circumflex over (b)} k ←v k /√{square root over (v k {circumflex over (b)})} k .  
 
   
   
     15. An apparatus for use in a base station associated with a cell of a cellular wireless communication system and having an antenna array, the apparatus comprising:
 a base station receiver coupled to the antenna array and operative: (i) to estimate a spatial covariance matrix for each of a plurality of mobile stations communicating with the base station, the spatial covariance matrix for a given one of the mobile stations being determined at least in part based on a unique hopping sequence of the mobile station and providing a correlation between signals received from the mobile station at different antenna elements within the antenna array; (ii) to process the estimated spatial covariance matrices to generate an estimate of an interference matrix for the plurality of mobile stations; (iii) to estimate an array response for the given mobile station from the interference matrix; (iv) to process the array response for the given mobile station to generate an antenna weighting associated with the given mobile station; and (v) to apply the antenna weighting to a signal received from the given mobile station in order to facilitate detection of a corresponding transmitted symbol.  
 
   
   
     16. An apparatus for providing adaptation of an antenna array in a base station associated with a cell of a cellular wireless communication system, the apparatus comprising:
 means for estimating a spatial covariance matrix for each of a plurality of mobile stations communicating with the base station, the spatial covariance matrix for a given one of the mobile stations being determined at least in part based on a unique hopping sequence of the mobile station and providing a correlation between signals received from the mobile station at different antenna elements within the antenna array;  
 means for processing the estimated spatial covariance matrices to generate an estimate of an interference matrix for the plurality of mobile stations;  
 means for estimating an array response for the given mobile station from the interference matrix;  
 means for processing the array response for the given mobile station to generate an antenna weighting associated with the given mobile station; and  
 means for applying the antenna weighting to a signal received from the given mobile station in order to facilitate detection of a corresponding transmitted symbol.  
 
   
   
     17. A method for providing adaptation of an antenna array in a base station associated with a cell of a cellular wireless communication system, comprising the steps of:
 determining a spatial covariance matrix for each of a plurality of mobile stations communicating with the base station, the spatial covariance matrix for a given one of the mobile stations being determined at least in part based on a unique hopping sequence of the mobile station and providing a correlation between signals received from the mobile station at different antenna elements within the antenna array; and  
 processing the estimated spatial covariance matrices to determine an antenna weighting associated with the given mobile station;  
 wherein the antenna weighting is applied to a signal received from the given mobile station in order to facilitate detection of a corresponding transmitted symbol; and  
 wherein the unique hopping sequence specifies for the given mobile station a hopping between tones of a plurality of orthogonal frequency division multiplexed tones, each of the mobile stations being assigned one or more of the tones for use in conjunction with transmission of a corresponding symbol, the tone assignments being changed for the mobile stations on a symbol-by-symbol basis.  
 
   
   
     18. An apparatus for use with a base station associated with a cell of a cellular wireless communication system and having an antenna array, the apparatus comprising:
 a base station receiver coupled to the antenna array and operative: (i) to determine a spatial covariance matrix for each of a plurality of mobile stations communicating with the base station, the spatial covariance matrix for a given one of the mobile stations being determined at least in part based on a unique hopping sequence of the mobile station and providing a correlation between signals received from the mobile station at different antenna elements within the antenna array; and (ii) to process the estimated spatial covariance matrices to determine an antenna weighting associated with the given mobile station;  
 wherein the antenna weighting is applied to a signal received from the given mobile station in order to facilitate detection of a corresponding transmitted symbol; and  
 wherein the unique hopping sequence specifies for the given mobile station a hopping between tones of a plurality of orthogonal frequency division multiplexed tones, each of the mobile stations being assigned one or more of the tones for use in conjunction with transmission of a corresponding symbol, the tone assignments being changed for the mobile stations on a symbol-by-symbol basis.  
 
   
   
     19. An apparatus for providing adaptation for an antenna array of a base station associated with a cell of a cellular wireless communication system, the apparatus comprising:
 means for determining a spatial covariance matrix for each of a plurality of mobile stations communicating with the base station, the spatial covariance matrix for a given one of the mobile stations being determined at least in part based on a unique hopping sequence of the mobile station and providing a correlation between signals received from the mobile station at different antenna elements within the antenna array;  
 means for processing the estimated spatial covariance matrices to determine an antenna weighting associated with the given mobile station; and  
 weight applying means for applying the antenna weighting to a signal received from the given mobile station in order to facilitate detection of a corresponding transmitted symbol;  
 wherein the unique hopping sequence specifies for the given mobile station a hopping between tones of a plurality of orthogonal frequency division multiplexed tones, each of the mobile stations being assigned one or more of the tones for use in conjunction with transmission of a corresponding symbol, the tone assignments being changed for the mobile stations on a symbol-by-symbol basis.  
 
   
   
     20. An apparatus for use with a base station associated with a cell of a cellular wireless communication system and having an antenna array, the apparatus comprising:
 a processor operative: (i) to determine a spatial covariance matrix for each of a plurality of mobile stations communicating with the base station, the spatial covariance matrix for a given one of the mobile stations being determined at least in part based on a unique hopping sequence of the mobile station and providing a correlation between signals received from the mobile station at different antenna elements within the antenna array; and (ii) to process the estimated spatial covariance matrices to determine an antenna weighting associated with the given mobile station;  
 wherein the antenna weighting is applied to a signal received from the given mobile station in order to facilitate detection of a corresponding transmitted symbol, and  
 wherein the unique hopping sequence specifies for the given mobile station a hopping between tones of a plurality of orthogonal frequency division multiplexed tones, each of the mobile stations being assigned one or more of the tones for use in conjunction with transmission of a corresponding symbol, the tone assignments being changed for the mobile stations on a symbol-by-symbol basis.